Molds for tire vulcanization are equipped with venting bores, through which air escapes, so that semi-finished tire placed in the mold by pressure acting from the side of mold cavity can acquire the shape corresponding to the tool inserted in the vulcanization mold. This unvulcanized semi-finished product moves the air to the mold circumference, where it escapes from the mold. At the same time the tire material enters the venting bores and projecting excess rubber results, which must be removed following the vulcanization.
Insufficient removal of air from the vulcanization mold causes faults on the finished products, both depressions are formed in the tread area and the material may be insufficiently heated and thus vulcanization of the semi-finished product may be incomplete.
Vent valves and vulcanization forms equipped with vent valves are known from EP 0774 333 (CZ 291837), where the vent valve for venting bore of the vulcanization mold contains a movable valve insert with a valve shank and a disk, wherein the valve insert may be pushed into the closed position by pressure acting on that side of the disk, which is oriented to the cavity of the vulcanization mold, into which the vent valve is built-in, and vice versa, the valve insert can be moved by means of a spring into an open position, if no pressure acting from the cavity on the valve disk is present, wherein movement of the valve insert is delimited by a stop, arranged at the end of the vent valve oriented away from the cavity, for restricting the valve insert movement into the open position to a path shorter than 2 mm, wherein, for the purpose of a possibility to dismount the valve insert, the stop is realized as a snap connection provided with a clearance between the valve shank at one hand and the valve body at the other hand. Delimitation of the vent valve path is ensured by the snap lock. The snap lock is preferably located on the valve shank or it is inserted into the valve body. A disadvantage of this solution is that the vent valve consists even of four components, namely of a valve body, a valve insert, a wound spring and a flexion spring, which represents the snap lock. Disassembly of some embodiments of the vent valve according to the invention is also problematic.
The aim of the present invention is to create such vent valve, which will provide for reliable air venting of a vulcanization mold, will consist of possibly the simplest parts, will be simply assembled and disassembled and simultaneously, its price will be acceptable.